Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

2. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

9: 1

1: 9

1: 3

3. For obtaining high COP, the pressure range of compressor should be

High

Low

Optimum

Any value

4. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.67

0.4

5. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Any one of the above

Always less than unity

6. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

7. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Rankine

Carnot

8. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

9. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

10. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

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11. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

None of these

Sub-cooling or under-cooling

Super-cooling

12. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

8 bar

2 bar

30 bar

13. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

3.33

2.33

14. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

15. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

16. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

17. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

18. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

19. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

0.1 ton

40 tons

20. The capillary tube, as an expansion device, is used in

Water coolers

All of these

Domestic refrigerators

Room air conditioners

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21. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Carnot

Ericson

22. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Evaporator

Absorber

23. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

24. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

25. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Zero

Positive

26. Critical temperature is the temperature above which

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

Water will never evaporate

27. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

28. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Miniature sealed unit

Axial

29. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Two heat exchangers

Three heat exchangers

30. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Condenser tubes

Refrigerant cooling tubes

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31. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

32. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dry bulb temperature

Dew point temperature

33. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Ammonia

Brine

34. Most thermostatic expansion valves are set for a superheat of

20°C

5°C

15°C

10°C

35. Freon group of refrigerants are

Non-inflammable and toxic

Toxic

Inflammable

Nontoxic and non-inflammable

36. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

37. The boiling point of ammonia is

-33.3°C

-10.5°C

-30°C

-77.7°C

38. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-77.7°C

-75.2°C

39. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

40. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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